glib: slist: how check if empty

[Felix Kater <f kater2 gmx net>]

Hi,

it could be helpful to add a note how to check if a slist is empty,
either in the general description or g_slist_remove() function (maybe
at both places).

E.g.: "When the last element is removed the pointer to slist is set to
NULL."

AFAIK this is not mentioned anywhere.

Felix